Organodiphosphites are known to be useful as ligands for metal-complex catalysts which are useful in hydrocyanation reactions. Particularly useful organodiphosphites are those of the general structure: EQU (RO).sub.2 P(OZO)P(OR).sub.2.
The synthesis of these organodiphosphites can be accomplished by reacting a mixture of at least one alcohol (ROH) and a diol (HOZOH) with phosphorous trichloride under conditions which allow resulting HCl to be distilled away, often at elevated temperature. This kind of synthesis can result in the production of a reaction product which also contains unwanted byproducts. These byproducts can include various organomonophosphites. These byproducts can also include unwanted organodiphosphites, including those of the formulae shown below: ##STR1## and ##STR2##
Depending upon the relative amounts of ROH and HOZOH in the alcohol/diol mixture, the reaction product of the alcohol/diol mixture and PCl.sub.3 may contain the desired organodiphosphite in unacceptably low yields.
In general, laboratory approaches to selectively producing organodiphosphites involve carrying out the reaction in the presence of a base such as trialkylamine under extreme cold conditions (e.g. -78.degree. C.). Although desired organodiphosphites can be produced, they can undergo molecular rearrangement in the presence of acid to yield unwanted byproducts. A combination of carrying out the reaction in the presence of a base and in extreme cold can effectively slow down rearrangement to allow for a selective synthesis of the desired organodiphosphites through sequential addition of the alcohols and diol.
However, extreme cold is impractical from a commercial viewpoint, and there have been attempts to carry out selective synthesis under more practical conditions. In WO96/22968, a multistep process for the synthesis of compounds of the type (ArO).sub.2 P(O--Z--O)P(OAr).sub.2 where Ar and Z are substituted or unsubstituted aryl groups is described in which all steps are carried out at 0.degree. C. or above with selectivity of about 90% reported. The process involves the synthesis of intermediate phosphoramidite compounds (RO).sub.2 P--N(R').sub.2, which are then converted to phosphorchloridites, (RO).sub.2 PCl, by reacting the phosphoramidites with anhydrous HCl, and then reacting the phosphorchloridites with base and the organic diol, HO--Z--OH, to produce the desired organodiphosphite.
U.S. Pat. No. 5,235,113 discloses a room temperature process for the preparation of a phosphite having a formula (RO).sub.2 P(O--A--O)P(OR).sub.2 where A is biphenyl and R is 3,6-di-t-butyl-2-napthyl. The process involves reacting a solution of 4 molar equivalents of 3,6-di-t-butyl-2-naphthol (an ROH material) and 4 molar equivalents of triethylamine (a base) with 2 molar equivalents of PCl.sub.3 by dropwise addition to produce a phosphorchloridite intermediate. This product is then reacted with one molar equivalent of 2,2'-biphenyldiol (an HOZOH) and 2 molar equivalents of triethylamine by dropwise addition.
U.S. Pat. No. 4,668,651 discloses a process for making certain symmetric organodiphosphites by reacting an organic diphenolic compound with phosphorous trichloride to form a phosphorochloridite intermediate and then reacting the intermediate with a diol.
The process of WO96/22968 produces acceptable products, but it is a relative high cost multistep process. The process of U.S. Pat. No. 5,235,113 is simple, but can result in low yields of certain organodiphosphites, depending on the nature of the ROH reactant.
It would be desirable to have a process for producing organodiphosphites in high yield, good selectivity and at a commercially desirable cost. These objectives are met by the process of the present invention.